Mercapturic acid pathway is one of the major defense mechanisms against the toxic effects of drugs, xenobiotics and pollutants. We have recently demonstrated that all the enzymes of mercapturic acid pathway are present in bovine ocular tissues. These enzymes namely glutathione S-transferase, Gamma-glutamyl transferase, dipeptidase and N-acetylase will be studied in human and bovine ocular tissues. These enzymes, particularly the multiple forms of gluthathione S-transferase, will be purified to homogeneity from human as well as bovine ocular tissue. Substrate specificities, kinetic properties and ligand binding characteristics of various GSH S-transferase isoenzymes will studied in order to assess their role in defense mechanisms. Structural, immunological and functional interrelationship among various isoenzymes of GSH S-transferases of human and bovine GSH S-transferases will be studied using homogenous isoenzyme preparations and antibodies raised against these preparations. GSH S-transferases are multifunctional proteins. In addition to their catalytic function, GSH S-transferases are believed to remove toxic alkylating compounds from the liver by binding them by 'suicidal action'. Binding between ocular GSH S-transferases and xenobiotics and drugs and their 'activated' metabolites will be studied to assess this role of GSH S-transferases in removing toxic compounds from ocular tissues. GSH S-transferases may also play an important role in protecting the membrane lipids from the deleterious effects of lipid hydroperoxides. Hydroperoxides formed from the unsaturated fatty acids and cholesterol can be decomposed by the S-transferases through their GSH peroxidase (GSH Px II) activity. GSH peroxidase II activity of various ocular GSH S-transferase isoenzymes in humans and bovine will be studied in order to evaluate the physiological significance of this activity. Recent studies in our laboratory indicate that the antioxidants, t-butylated hydroxy toluene (BHT) and t-butylated hydroxy anisol (BHA) induce GSH S-transferase and GSH in rat liver, lung, and kidney. The effect of these antioxidants on GSH-linked detoxification mechanisms of ocular tissues in rats and mice will also be studied. These studies will be eventually helpful in finding ways to negate the toxic effects of various drugs, xenobiotics and endogenous lipid hydroperoxides in the ocular tissue.